Wireless communication systems are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These systems may be multiple-access systems capable of supporting multiple users by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal FDMA (OFDMA) systems, and Single-Carrier FDMA (SC-FDMA) systems.
Wireless communication networks are based on the OSI reference model and are organized as a series of layers with well-defined interfaces, and with each layer built on its predecessor. Each layer performs a related subset of functions and relies on the next lower layer to perform additional functions. Moreover, each layer offers certain services to the next higher layer. Individual layers on one system communicate with respective layers on another system in accordance with a set of rules and conventions constituting a layer protocol. Except from the physical layer, where a physical link exists between the transmitter side and the receiver side of the corresponding layers, all other layers are in virtual communication with their distant peers, forming logical links. These links, logical or physical, are characterized, among other things, by throughput and latency.
Throughput or network throughput is the average rate of successful data packet delivery over a communication channel. This data packet may be delivered over a physical or logical link, or pass through a certain network node. Throughput is usually measured in bits per second (bit/s or bps), and sometimes in data packets per second or data packets per time slot. Latency, on the other hand, is the time taken for a sent data packet to be received at the other end. It includes the time to encode the packet for transmission and transmit it, the time for that data to traverse the network equipment between the nodes, and the time to receive and decode the data.
Many wireless systems, such as the EV-DO system, use the Radio Link Protocol for network-based error corrections to ensure robust data transmission. RLP is designed to optimize the performance data flows for an upper layer, typically an application layer, crossing the wireless link, especially to maximize the utilization of the link. RLP uses packet retransmission to hide the errors at the physical or the MAC layers from the upper layers, presenting a very low error rate to the application layer. At the same time RLP strives to minimize the link end-to-end latency to keep the link throughput as close as the PHY throughput as possible. Both error rate and latency greatly affect TCP performance.
For the most part RLP achieves its goal effectively. There are conditions however where RLP doesn't perform optimally. For example in the presence of packet reordering, RLP tends to assume packet loss and hence trigger unnecessary retransmissions. Similarly, in the presence of high error rate, either at the MAC or the physical layer, the physical layer of a wireless wide area network (WWAN) link is characterized by a frame error rate higher than what typical data application can tolerate.
For example, WWAN supporting TCP/IP data packets cannot tolerate data packet loss without significant throughput degradation. WWAN technology usually addresses this issue with retransmission-based reliability schemes that hide most of the errors from TCP/IP. Such an example is RLP in EV-DO.
If a WWAN system is tuned to operate in a regime where the physical error rate is higher than the standard's settings (1%), the residual error rate presented to RLP would be such that multiple RLP retransmissions could be necessary to present an acceptable error rate at the upper (application) layer. This would significantly increase the latency of the WWAN performance.
Optimization of the operation of upper layer protocols (such as TCP) remains a goal of an improved RLP protocol. Any new RLP protocol should provide: (i) reduced sensitivity to packet reordering, (ii) larger physical error rate operating range, (iii) more consistent latency in the presence of packet loss and/or reordering, (iv) simpler design and (v) good response to burst losses caused, for example, by changing the Serving Sector (cell re-pointing).
To facilitate understanding, identical reference numerals have been used where possible to designate identical elements that are common to the figures, except that suffixes may be added, where appropriate, to differentiate such elements. The images in the drawings are simplified for illustrative purposes and are not necessarily depicted to scale.
The appended drawings illustrate exemplary configurations of the disclosure and, as such, should not be considered as limiting the scope of the disclosure that may admit to other equally effective configurations. Correspondingly, it has been contemplated that features of some configurations may be beneficially incorporated in other configurations without further recitation.